Coupling process for substituted aminoazobenzenesulfonic acids

ABSTRACT

An arylaminosulfonic acid is diazotized in a mineral acid with sodium nitrite, the pH at completion of diazotization being below about 0.5. An aryl, primary amino-group-containing coupler is added to the diazotization mass and coupling to the benzene ring completed in at least three stages by gradually raising the temperature to 20*-30*C., maintaining a pH below 1.5.

United States Patent 1 Bellettini et al.

[ June 3, 1975 COUPLING PROCESS FOR SUBSTITUTED AMINOAZOBENZENESULFONIC ACIDS Inventors: Arturo Gabriel Bellettini, Newark;

Richard Crawford Franklin, Wilmington, both of Del.

Assignee: E. l. du Pont de Nemours and Company, Wilmington, Del.

Filed: Nov. 23, 1971 Appl. No.: 201,567

US. Cl 260/205; 260/206 Int. Cl. C07c 107/06; C09b 29/08;

C09b 29/26 Field of Search 260/205, 206, 175

References Cited UNITED STATES PATENTS 12/1938 Biswell et al 260/205 3,485,814 12/1969 Speck 260/184 X Primary Examiner-Floyd D. Higel Assistant Examiner-C. F. Warren Attorney, Agent, or Firm-James A. Costello; Theodore C. Gregory [5 7] ABSTRACT 2 Claims, No Drawings COUPLING PROCESS FOR SUBSTITUTED AMINOAZOBENZENESULFONIC ACIDS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for the direct ring coupling of diazonium salts to primary amines. More specifically, this process relates to a process for the direct ring coupling of diazonium salts of arylamine sulfonic acids to ortho-anisidine and ortho-toluidine.

2. Description of the Prior Art Ring coupling of a diazonium salt to certain aromatic primary amines such as aniline, o-toluidine and oanisidine proceeds slowly, and frequently gives the diazoamino compound or a mixture of products. The desired ring-coupled azo product is ordinarily not obtained in good yield or quality. The prior art avoids the difficulty by complexing the amino group with a formaldehyde sodium bisulfite adduct to give the so-called omega salt. After coupling to the omega salt, the complex is broken by reaction with alkali or acid to free the amino group of the azo product. The process is illustrated in the following equations:

1. HCHO NaHSO HOCH SO Na It is also known that diazonium salts can be coupled directly to certain primary aryl amines such as mtoluidine, 2,4-Xylidine and others under acidic conditions to give the desired ring-coupled products in good yield. However, the amines of the present invention and the diazonium salts of the present invention cannot be coupled by such a method to give high yields and high purities by the usual procedures.

It is an object of the present invention to provide an improved process for the direct ring coupling of diazonium salts to primary aryl amines. It is also an object of the present invention to provide a process for the direct ring coupling of diazonium salts'to primary aryl amines at low controlled pH range. It is still further an object of the present invention to provide an improved process for the production of dye intermediates in high yields and high purity. These and other objectives will be apparent from the disclosure that follows.

SUMMARY OF THE INVENTION In accordance with the invention it has been found that direct ring coupling of aryl sulfonic acid diazonium salts to primary aryl amines is achieved by a process conducted at a temperature of from about 5C. to about 30C. wherein pH is controlled at from about 0.2 to about 1.5. Accordingly, in the process of couplingan aryl sulfonic acid diazonium salt selected from the group consisting of a metanilic acid diazonium salt and a sulfanilic acid diazonium salt to aprim'ary aryl amine selected from the group consisting of ortho-anisidine, ortho-toluidine and aniline, the improvement wherein the coupling is performed at a pH of from about 0.2 to about 1.5 and a temperature of from about 5C. to about 30C. was discovered.

Ring coupling of an aryl diazonium salt to many aromatic primary amines takes place very slowly, giving a very poor yield and a complex mixture of byproducts. Stabilizing these aromatic primary amines by complexing the amino group with a formaldehyde-bisulfite addition compound to form an omega salt before coupling was disclosed in German Pat. No. 131,860 in 1899. This process has been widely used ever since. The present process involves the direct coupling of diazonium salts to such aromatic primary amines with satisfactory yields and purity of product. The process of this invention avoids the prior art necessity of preparing the omega salt derivative of the amino group bearing coupling compound, and its eventual hydrolysis to yield the desired product. The coupling process of the invention is performed at an initial pH of about 0.2 to 0.5. The pH is raised as reaction progresses by adding a mild alkali. The temperature is gradually increased from a starting 515C. to a final 2030C.

The aryl sulfonic acid diazonium salts of this invention include diazo salts of aminobenzenesulfonic acids and substituted aminobenzenesulfonic acids. The preferred diazo salts are those derived from sulfanilic acid and metanilic acid.

The diazotization of the aminobenzenesulfonic acids is well known in the art and may be performed essentially as indicated in US. Pat. No. 1,538,934.

Details of the coupling procedure can be varied somewhat to suit the activity of the particular diazo compound and coupler employed. The coupling procedure of this invention involves a series of stages. The coupler is normally added to the diazotization mass over a short period of time, usually 15 minutes to an hour, maintaining temperature at below 15C., preferably 510C. The ph at this stage must be below 0.8 and is usually about 0.5 or lower. This condition is maintained for about four hours, although this time is not critical and may be extended if desired. A milk alkali is then added carefully with good mixing to avoid local over-concentration until pH reaches 0.8 i .2. Temperature is then allowed to rise over 1 to 4 hours to about 20C. It may be necessary to add more alkali to maintain pH at 0.8, as the pH tends to fall as reaction progresses. In the third stage of the' process the charge is stirred for an extended period of 8 to 16 hours with temperature at 20-25C. to complete the reaction. In some cases, where less active couplers are employe the temperature may be allowed to go higher, to 3035C. During the extended final reaction period the pH tends to fall, and is readjusted to near 0.8. Finally a little more acid is added, and the solid product isolated in a filter. It is washed with weak acid to remove any residual diazo compound, which if Present might tend to ignite during subsequent drying.

cally attractive. The precise control of pH disclosed in this invention gives a superior yield and purity of the desired azo product over processes merely disclosing coupling in an acid medium.

The primary aryl amine couplers of this invention are ortho-anisidine, ortho-toluidine and aniline. A preferred coupler is ortho-anisidine.

The following examples further illustrate the invention. All percentages and parts therein are by weight unless otherwise stated.

EXAMPLE 1 In a suitable vessel 23.1 parts of sodium metanilate were dissolved in water to make a 33.0 percent solution, and 9.2 parts of sodium nitrite were added as 30 percent solution. A separate vessel was then charged with 17.0 parts of water and 19.7 parts of hydrochloric acid as 30 percent acid. Sufficient ice was added to cool the mass to between 5 and C. With good agitation the metanilate-nitrite solution was then added to the acid over a 45 minute period, keeping the temperature below C. by adding more ice as necessary. An excess of nitrite was maintained, with pH below 1.5 for an hour after all of the metanilate-nitrite solution had been added. A little 10 percent aqueous sulfamic acid solution was then added to decompose the remaining excess nitrous acid. Still maintaining the temperature at 10-15C., 18.08 parts of orthoanisidine were added over a 15-20 minute period to the metanilic acid diazo slurry. Most of the diazo appeared to dissolve, and the product began to appear as a dark red solid. The mass was stirred for four hours at about l0-15C., ice being added as necessary. The pH during this period remained below 0.5. Zinc oxide powder was then added over a one hour period sufficient to raise the pH to about 0.8, maintaining temperature at l2-l5C. About 5.5 parts of zinc oxide were required. The charge was stirred for four more hours as the temperature gradually rose to about C. During this period the pH dropped slightly, while viscosity of the mass decreased quite noticeably. The pH was maintained at 0.8 i 0.2 by adding additional small quantities of zinc oxide. For a second four hour period the temperature was allowed to rise to C., then the charge was held at 25C. and pH 0.8 for 8-16 hours. Next 1.0 part of 100 percent hydrochloric acid was added (in the form of percent aqueous solution) to bring pH to below 0.5, and the solid was removed by filtration. The solid product was washed thoroughly with 1 percent hydrochloric acid to remove any residual diazo compound. The product was removed from the filter and analyzed for percent solids and purity (by TiCl titration). Yield was about 55 percent of theory.

EXAMPLE 2 Metanilic acid was coupled to ortho-toluidine Using the same general procedure as described in Example 1, a solution was prepared of 63.8 parts water, 73.8 parts HCl (in the form of 30 percent hydrochloric acid), and a separate solution of 86.6 parts of sodium metanilate and 35.2 parts of sodium nitrite (in the form of 30 percent aqueous solution). The nitrite and metanilate were added to the hydrochloric acid solution at 8-10C. over one-half hour, then stirred an additional hour. A little sulfamic acid solution was added to decompose the excess nitrous acid. To the diazo solution at 0C. there were added 58.9 parts of orthotoluidine over about 20 minutes. The mass was stirred at 0C. with pH at about 0.5 for three hours. Then 20 parts of zinc oxide were added to raise the pH to 0.8. The charge was then stirred for 16 hours (overnight) with temperature between 0 and 8C. The pH ranged between 0.3 and 0.6, being adjusted by adding a little more zinc oxide. Then 0.37 parts of percent HCl (as 30 percent hydrochloric acid) were added and the solid was filtered off and washed as in Example 1 with 1 percent hydrochloric acid. Yield was 60.5 parts of m- (4-amino-3-methylphenylazo)benzenesulfonic acid.

EXAMPLE 3 Sulfanilic acid was diazotized and coupled directly to orthoanisidine A solution was prepared of 68.6 parts water, 25.98 parts of sulfanilic acid and 22.14 parts of 100 percent HCl (as 30 percent hydrochloric acid), then 10.56 parts of sodium nitrite (as 30 percent solution) were added over one-half hour with temperature at 810C. After one hour of stirring with a slight excess of nitrite, a small amount of sulfamic acid was added to decompose the excess nitrous acid, and 20.3 parts of orthoanisidine were added over 5-10 minutes with temperature at 810C. The mass was stirred for one hour with pH at 0.5-0.0. Then 5.0 parts of zinc oxide were added and the charge stirred an additional two hours with pH at about 0.2 and temperature at 15C. Another 5.0 parts of zinc oxide were added, bringing the pH to 0.8. The temperature was allowed to rise to 25C. and the charge stirred for 16 hours. The final pH was 0.7. Then 1.1 parts of 100 percent HCl (as 30 percent hydrochloric acid) were added and the solid product isolated by filtration. It was washed as before with 1 percent hydrochloric acid. Yield of p-(4-amino-3-methoxyphenylazo)benzene sulfonic acid was 58.3 percent of theory.

EXAMPLE 4 Sulfanilic acid was diazotized and coupled directly to orthotoluidine A solution was prepared of 17.1 parts of water 8.66 parts of sulfanilic acid and 2.0 parts of NaOH (as 30 percent solution) and 3.52 parts of sodium nitrite (as 30 percent solution). This solution was added over 30 minutes to a mixture of 6.38 parts of water and 7.38 parts of HCl (as 30 percent hydrochloric acid) held at l015C. The mass was stirred for 30 minutes, then a little sulfamic acid solution was added to decompose residual excess nitrous acid. There were then added 6.77 parts of ortho-toluidine over 5l0 minutes, mamtaining temperature at 1015C. The mass was stirred for two hours at pH 0.0-0.2 and l0l5C. Sufficient zinc oxide was added to raise the pH to 0.8 about 1.5 parts were required. The temperature was allowed to rise slowly to 25C. and the charge stirred overnight. The pH had dropped to 0.4. Finally 0.375 parts of 100 percent HCl (as 30 percent hydrochloric acid) were added and the charge was filtered to isolate the solid product. It was washed as before with 1 percent hydrochloric acid. Yield was 3.69 parts of p-(4-amino-3- methylphenylazo)benzene sulfonic acid or 23.5 percent of theory.

When the above example was repeated without the addition of ZnO and final adjustment of pH, there was no solid product isolatable.

EXAMPLES pH adjustment made with sodium acetate rather than zinc oxide Metanilic acid was diazotized and coupled to orthoanisidine according to the procedure of Example 1. After coupling was complete the mass was held at pH .7 for an hour, then sodium acetate was added to raise the pH to 0.8 and the temperature was allowed to rise from C. to 20-22C. over two hours. With pH at 0.8 and temperature at 22-25C. the charge was stirred for 16 hours, when pH had dropped to 0.3. The charge was further acidified and filtered and washed as in the other examples. Yield was 51.8 percent of theory.

EXAMPLES 6 and 7 The procedure of Example 5 was repeated, substituting ammonium hydroxide for the sodium acetate of Example 5 in one case, and substituting triethanolamine in the other. The pH adjustments were carried out as before, followed by the same isolation procedure. Yields were 47.1 percent of theory in the triethanolamaine adjusted run and 52.5 percent of theory in the ammonium hydroxide adjusted run.

EXAMPLE 8 In this example nitric acid was used as diazotization medium instead of hydrochloric acid. A mixture was made of 23.55 parts of water, 12.75 parts of HNO (as 60 percent nitric acid) and cooled to about 10C. There were then added over a one-half hour period a solution of 8.66 parts of sodium metanilate and 3.52 parts of NaNO (as 30 percent aqueous solution). After one-half hour a little sulfamic acid was added to decompose excess nitrous acid. Next 6.77 parts of orthoanisidine were added over minutes. With pH at 0.1 the charge was stirred for one hour, then 1.5 parts of zinc oxide were added to raise the pH to 0.8. The product slurry was thinner than in similar runs where hydrochloric acid was used. The temperature was allowed to rise from 10C. to -22C. over several hours, and the charge stirred for 16 hours at that temperature. At the beginning of the stirring period pH was 0.8, while at the end pH was 0.2. Then 0.375 parts of HCl (as 30 percent solution) were added and the solid separated by filtration. It was washed free of diazo with 1 percent hydrochloric acid, as before. Yield was 8.59 parts, equal to 52 percent of theory.

The concentration of reactants in the process of this invention may vary widely. Through the use of external diazotization was varied from 7.5-14.35 parts per parts of total coupling mass. Concentrations of 7.5-9.25 parts of metanilic acid per 100 parts of coupling mass yielded methoxyaminoazobenzenesulfonic acid amounting to 45-50 percent of theoretical. Concentrations of 12.0-14.0 parts of metanilic acid per 100 parts of coupling mass yielded methoxyaminoazobenzenesulfonic acid amounting to 60-65 percent of theoretical. Thus the preferred concentration range is 12.0-14.0 parts of aryl sulfonic acid diazonium salt. The optimum yields obtained from the above preferred concentrations are not always attainable when using ice for cooling due to the resulting dilution.

The azo compounds which are the products of the process of this invention are useful as dyes and dye intermediates. They are particularly useful for preparing disazo dyes containing a diphenylurea nucleus. Such dyes are prepared by reacting 2 molecules of the azo compound with 1 molecule of phosgene. A mixture of azo compounds can be used. US. Pat. No. 935,016 discloses such a process for the preparation of dyes from the azo compounds of this invention at lines 25-44. Additionally, the Color Index Dye discloses the preparation of Color Index Dye CI. 29000 by reacting the azo producst of Example 1 with phosgene to produce C.l. Direct Yellow 44.

The foregoing detailed description has been given for clarity of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to exact details shown and described for obvious modifications will occur to one skilled in the art.

What is claimed is:

1. 1n the process of coupling metanilic acid diazonium salt or sulfanilic acid diazonium salt directly to the ring of a pripmary aryl amine under acidic conditions, the improvement insisting essentially of coupling to a primary aryl amine selected from the group consisting-of ortho-anisidine, ortho-toluidine, and aniline, at a pH between 0.2 to 1.5 and at a temperature from about 5C. to 30C., wherein the initial pH is about 0.2 to 0.5 and is raised as reaction progresses by adding mild alkali and the initial temperature is about 5C. to 15C. and is gradually raised to about 20C. to 30C.

2. The process according to claim 1 consisting essentially of, in sequence,

i. adding the primary aryl amine to the diazonium salt at a temperature of about 5C. to 15C.

and at a pH of about 0.2 to 0.5,

ii. adjusting the pH to 0.8 1 0.2, and the temperature to about 20C., and

iii. stirring the reactants until the reaction is complete, at a temperature of about 20C. to 25C. and at a pH of about 0.8. 

1. In the process of coupling metanilic acid diazonium salt or sulfanilic acid diazonium salt directly to the ring of a pripmary aryl amine under acidic conditions, the improvement insisting essentially of coupling to a primary aryl amine selected from the group consisting of ortho-anisidine, ortho-toluidine, and aniline, at a pH between 0.2 to 1.5 and at a temperature from about 5*C. to 30*C., wherein the initial pH is about 0.2 to 0.5 and is raised as reaction progresses by adding mild alkali and the initial temperature is about 5*C. to 15*C. and is gradually raised to about 20*C. to 30*C.
 1. IN THE PROCESS OF COUPLING METANILIC ACID DIAZONIUM SALT OR SULFANILIC ACID DIAZONIUM SALT DIRECTLY TO THE RING OF A PRIPMARY ARYL AMINE UNDER ACIDIC CONDITIONS, THE IMPROVEMENT INSISTING ESSENTIALLY OF COUPLING TO A PRIMARY ARYL AMINE SELECTED FROM THE GROUP CONSISTING OF ORTHO-ANISIDINE, ORTHOTOLUIDINE, AND ANILINE, AT A PH BETWEEN 0.2 TO 1.5 AND AT A TEMPERATURE FROM ABOUT 5*C. TO 30*C., WHEREIN THE INITIAL PH IS ABOUT 0.2 TO 0.5 AND IS RAISED AS REACTION PROGRESSES BY ADDING MILD ALKALI AND THE INITIAL TEMPERATURE IS ABOUT 5*C. TO 15*C. AND IS GRADUALLY RAISED TO ABOUT 20*C. TO 30*C. 